Current commercially available lithium batteries use electrolytes including combustible organic solvents, and therefore, installing safety devices that suppress temperature increases in short circuits, improving structures for short circuit prevention, and improving materials for the structural improvement may be required. Accordingly, all solid batteries that do not use combustible organic solvents in the battery structure have been considered to provide simplified safety devices and improved productivity.
Electrodes of all solid lithium batteries typically use a mixture of solid electrolyte materials to increase the conductivity of lithium ions. For example, in the related art, a solid electrolyte lithium secondary battery has been provided by laminating an anode electrode in which an anode clad sheet layer containing anode active material powder and solid electrolyte powder, a solid electrolyte layer (SE), and a cathode electrode sequentially on both sides of a plate-shaped anode current collector. Therefore, a solid electrolyte having high adhesion between an anode and a cathode electrode may be provided within the battery, and the bending or cracks of batteries due to the expansion and the contraction of the anode and the cathode electrode accompanied with charge and discharge may be reduced.
Many solid lithium batteries may be one of the next generation batteries which require substantially high capacity and high output. In one example, an electrode active material layer may be thickened to obtain the higher capacity. However, the output property may be deteriorated due to the resistance increase by the thickening.
Meanwhile, in the related art, a solid battery has been developed to improve an output property by reducing the diffusion resistance of lithium ions with a composition distribution, in which an active material volume ratio increases as being closer to a solid electrolyte interface based on the thickness direction. For example, as shown in FIG. 1, an electrode in which an anode active material layer is divided into two sections and an anode active material layer 2 has a higher solid electrolyte ratio than an anode active material layer 1. In this example, the process of preparing an electrode having different material ratios may go through several steps to increase electrode density, such as a rolling process which may be performed after coating each layer having different material ratios, and the rolling process may then be repeated. Particularly, the layers may be limited to a layer having a high anode material ratio and a layer having a high solid electrolyte material ratio when two layers are formed. In addition, continuous concentration change may be applied to the layers, but specific examples or preparation method implications have not been provided as far.
The above information disclosed in this Background section is merely for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.